In discussing threats to biodiversity it is important to keep in mind that, behind these direct drivers of biodiversity loss, there are a number of indirect drivers that interact in complex ways to cause human-induced changes in biodiversity. They include demographic, economic, socio-political, cultural, religious, scientific and technological factors, which influence human activities that directly impact on biodiversity.

Indicators for trends in nutrient loading and invasive alien species have been identified under the focal area addressed here, and are described below. Information on habitat change is provided by the indicator trends in extent of selected biomes, ecosystems and habitats (see page 23). Overexploitation is discussed under the focal area on sustainable use (see page 36). While there is no single indicator of the impacts of climate change on biodiversity, a number of indicators, including those on trends in extent of selected biomes, ecosystems and habitats (particularly applied to coral reefs, polar ice and glaciers, and certain types of forests and drylands), abundance and distribution of selected species (see page 25), and incidence of human induced ecosystem failure, can serve to derive trends where specific data are available. Because small, fragmented ecosystems are more affected by changes in temperature and humidity than large contiguous ecosystems with a more balanced micro-climate, trends in connectivity/fragmentation of ecosystems (see page 30) provide an indicator of the vulnerability of ecosystems to climate change.

6.1 How are human activities affecting the amount of nitrogen in the environment?

The source document for this Digest states:

HEADLINE INDICATOR Nitrogen deposition

The ability of agriculture to produce far greater quantities of food and fibre than ever before can be attributed to a number of factors, including the availability of fertilizers on a commercial scale. However, excessive levels of the plant nutrients nitrogen and phosphorus in natural ecosystems are now causing concern. While reactive nitrogen occurs naturally in all ecosystems, the production of reactive nitrogen by humans, mostly from manufacturing synthetic fertilizer to increase agricultural production, has changed ecological balances, both locally and in far-distant ecosystems. Anthropogenic production of reactive nitrogen leads to the release of nitrogen compounds into the atmosphere, which are subsequently deposited onto the biosphere. Aerial deposition of nitrogen increases levels in ecosystems such that those slow growing species that thrive in nitrogen-poor environments cannot compete with faster-growing species that depend on higher nutrient levels. Temperate grasslands are particularly vulnerable in this respect. Moreover, soluble nitrogen leaches from soils into groundwater, resulting in increased eutrophication—excess nutrients in inland and coastal waters that stimulate excessive plant growth—algal blooms and the creation of anoxic (oxygen-free) zones in inshore marine areas.

Anthropogenic sources of nitrogen—from the manufacturing of synthetic fertilizer, fossil fuel combustion and by nitrogen-fixing crops and trees in agroecosystems—now exceed natural terrestrial sources, such that more than half of all reactive nitrogen in ecosystems globally now comes from human sources. The rate of increase in the production of reactive nitrogen has accelerated sharply since 1960 (Figure 2.15). Atmospheric deposition currently accounts for about 12% of the reactive nitrogen entering terrestrial and coastal marine ecosystems globally, although in some regions, this percentage is much higher (Figure 2.16).

To continue to meet global demand for food and fibre and minimize environmental problems, significant improvements are required in the efficiency with which nitrogen fertilizer is utilized within production systems. A 20% increase in nitrogen-use efficiency in the world’s cereal production systems would reduce the global production of reactive nitrogen by approximately 6% and lead to reduced expenditure for fertilizers equivalent to a value of about US$ 5 billion annually.

6.2 How serious is the threat to biodiversity posed by invasive alien species?

Invasive alien species can have devastating impacts on native biota, causing extinctions and affecting natural and cultivated ecosystems. Since the 17th century, invasive alien species have contributed to nearly 40% of all animal extinctions for which the cause is known. In the Fynbos biome of South Africa, 80% of the threatened species are endangered because of invading alien species.

A proportion of invasive alien species are important pests or pathogens that can cause enormous economic costs. The annual environmental losses caused by introduced pests in the United States, United Kingdom, Australia, South Africa, India and Brazil have been calculated at over US$ 100 billion. Invasive alien species can transform the structure and species composition of ecosystems by repressing or excluding native species. Because invasive species are often one of a whole suite of factors affecting particular sites or ecosystems, it is not always easy to determine the proportion of the impact that can be attributed to them. In the recent past, the rate and risk associated with alien species introductions have increased significantly because human population growth and human activities altering the environment have escalated rapidly, combined with the higher likelihood of species being spread as a result of increased travel, trade and tourism.

A major source of marine introductions of alien species is hull fouling and the release of ballast water from ships, although other vectors, such as aquaculture and aquarium releases, are also important and less well regulated than ballast water. In the marine ecosystem, the movement of non-native species has been well studied. Of the 150 species that have recently arrived in the Great Lakes, 75% originated from the Baltic Sea. Similarly, migration flow from the Red Sea to the Mediterranean through the Suez Canal continues unabated with nearly 300 species of these Lessepsian migrants, including decapod crustaceans, molluscs and fishes, having entered the Mediterranean since 1891.

Equally long-term data available from five Nordic countries (Iceland, Denmark, Norway, Sweden and Finland) that have recorded the cumulative number of alien species in freshwater, marine and terrestrial environments since 1900 demonstrate the continuing arrival of new immigrants of plants, vertebrates and invertebrates (Figure 2.17).

Invasive alien species are a global problem requiring responses at all levels. Many countries have established systems to prevent and control invasive alien species and, as part of risk assessments, to predict the likelihood of alien species becoming invasive and the potential ecological and economic cost they may incur. To effectively communicate the challenges posed by invasive alien species there is a need to develop a methodology for integrating information quantifying the threat and its impacts on biodiversity into a coherent indicator.